The only major allied nation that lost land after world war 1 was Russia

That´s correct.

Explanation:

The Russian army performed terribly in the battles of the Eastern Front, allowing German and Austrian advances. WWI led to chaos, famine and political agitation in Russia. The czarist government fell in February 1917. The democratic temporary government fell in November 1917. The Bolshevik government signed the disadvantageous Treaty of Brest-Litovsk in 1918. Russia lost one third of its territory and half of its population, and got out of the war.

a and b because with the other three, they simplify to something else.